#include <stdio.h>
#include <math.h>
/*
int main(){
	int arr[10]={8,1,6,7,2,7,2,5,218,562};
	for(int i=0;i<9;i++){
		for(int j=i+1;j<10;j++){
			if(arr[i]>arr[j]){
				int t=arr[i];
				arr[i]=arr[j];
				arr[j]=t;
			}
		}
	}
	for(int i=0;i<9;i++){
		printf("%d ",arr[i]);
	}
}*/
int main()
{
	int flag=0;
	int arr[4]={1,2,3,4};
	int x=0;
	scanf("%d",&x);
	int begin=0;
	int tail=3;
	while(begin<=tail){
		int mid=(begin+tail)/2;
		if(x<arr[mid]){
			tail=mid-1;
		}
		else if(x>arr[mid]){
			begin=mid+1;
		}
		else{
			printf("ok");
			flag=1;
			break;
		}
	}
	if(flag==0)
	printf("buok");
}
